Display both internal/external embed options

[thomaswilburn]

Internally, we have a Pym embed built into the CMS, so we only need the URL. However, for external partners, we need to send them a Sidechain HTML snippet. It can be a pain to translate between them, especially if there are multiple embeds in a graphic. We should have a toggle that lets you pick the embed format, and shows you whichever one you choose. This may also be a chance to rethink the bottom of the parent page, and make it more modular and/or load more of it from a single file instead of having preset "chunks" that we have to handle.